The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
In a satellite-based positioning system, such as the U.S. Global Positioning System (GPS), the Russian GLObal NAvigation Satellite System (GLONASS), the Chinese BeiDou-2 Navigation System (BDS), or a positioning system implemented based on a time-of-arrival (TOA) principle, a satellite positioning receiver receives broadcasted navigation data and ranging codes from multiple satellites detectable by the receiver and determines an estimated position of the receiver with respect to the transmitting satellites based on the received navigation data and ranging codes. In many positioning systems, navigation data are organized as a superframe, which can be divided into data frames and may be further divided into sub-frames. In many positioning systems, each sub-frame may include a predetermined bit sequence usable for indicating the boundaries of the sub-frames. The predetermined bit sequence is usually referred to as frame synchronization bits or a frame synchronization sequence (or simplified as a synchronization sequence in this disclosure), and a data word containing the frame synchronization sequence is usually referred to as a frame synchronization word (or simplified as a synchronization word in this disclosure).
Moreover, an indicator of the performance of a satellite positioning receiver is the Time-to-First-Fix (TTFF). The TTFF measures how long it takes a receiver to provide an estimated position after being activated. In some applications, the TTFF depends on many factors, including how long the receiver takes to successfully identify the frame synchronization sequence from the received navigation signals. When the signal strengths of the received navigation signals are weak or the signal quality thereof is substandard due to blocked signal paths, multipath interferences, or the like, the satellite positioning receiver may spend a significant amount of time trying to identify the frame synchronization sequence, and thus the TFTT may be increased.